1. Field of Invention
The present invention relates generally to agricultural tillage tools, and, more specifically, to an improved spring trip standard and bracket assembly for deep tillage applications where operating depths are less than that of typical ripper standards but greater than that of conventional field cultivator standards.
2. Related Art
Spring trip or spring cushion standard assemblies such as shown in U.S. Pat. No. 4,463,813 utilizing a single spring provide a cost effective arrangement and an advantageous trip/reset curve with a relatively high initial trip force for stability and elimination of unwanted tripping. U.S. Pat. No. 4,530,406 shows another example of a single spring standard assembly. However, some applications require standards to operate at depths less than that of typical ripper standards but greater than that of conventional field cultivator or chisel plow spring trip standards. Many of the standards have insufficient initial trip force to operate effectively at such depths, which may be as great as 13 inches. The standards must be able to trip at least as high as operating depth to clear obstacles so that trip height cannot be sacrificed in the design to achieve high initial trip force. A toggle trip design, which has the advantage of requiring less total energy for a given trip load/trip height, is often utilized with deep tillage standards. The disadvantage is that the reset force drops off considerably just after the toggle trips, which is not generally desirable. However, when designing standards with large trip loads and trip height requirements, the toggle trip was often the only practical solution.
To keep the required spring energy to a workable range in a spring trip standard, the trip load or the trip height must be minimized. The trip height requirement is driven by operating depth and therefore cannot be reduced. Therefore, the trip load must be minimized. Trip load is traditionally measured as a horizontal force at the tool tip or attaching point, which is satisfactory when analyzing loads resulting from the striking a solid obstacle. However, under normal operating conditions, the draft load has some vertical component which affects the overall resultant line of draft.
Increasing the initial trip force of a spring trip standard can be achieved by moving the tool attaching end rearwardly relative to the standard attaching pivot so that the resultant line of draft moves closer to the pivot, thereby reducing the resultant moment generated by draft force. The amount that the tool attaching end can be moved rearwardly, however, is limited by frame design considerations. If the standards are lengthened too much, they will not fit into the space allotted on the frame.
Increased spring energy can also be used to increase initial trip force of a spring trip standard. A single spring standard design, however, fails to provide sufficient increasing reset force for the first part of the trip cycle with sufficient resistance to avoid tripping when no obstacle is encountered. High torsional loads on the standard spring bracket develop when two springs are mounted side by side. An offset bracket with bends has to be used to accommodate the added width of a second spring, and whenever an offset part is loaded generally parallel with the offset bend lines, a twisting action is established. The torsional loads cause high stresses along the outer edges of the bracket in the area of the bends. The bracket can be made thicker to withstand these stresses, but such a thick component becomes expensive and impractical to manufacture.
A standard designed for intermediate operation down to a depth of about 13 inches should be able to lift and shatter soil in the manner of a typical parabolic ripper standard. The ripper standards, although having the desired shape, are heavier and more expensive than required for such intermediate tillage operations.